Accommodating Intraocular Lenses were developed in the early 1900's and have been sold in Europe for the last ten years and later in the U.S. They function by means of forward movement of the optic upon constriction of the ciliary muscle which increases the pressure in the posterior part of the eye with a simultaneous decrease in pressure in the front part of the eye pressure. The reverse pressure changes take place upon relaxation of the ciliary muscle, which results in the backwards movement of the lens for distance vision. The forward movement of the lens optic enables the patient implanted with the lens to automatically change their vision from distance to see at intermediate and near.
The currently marketed accommodating plate haptic intraocular lenses provide excellent distance and intermediate vision but sometimes require weak, +1.00, reading glasses for prolonged reading, for seeing small print, or reading in dim lighting conditions. The embodiments relating to the present invention presented herein are designed to substantially reduce the need for any reading glasses.
It is important for intraocular lenses to have a consistent location along the axis of the eye to provide good uncorrected distance vision and to center in the middle of the vertical meridian of the eye. Without excellent uncorrected distance vision there is no point in implanting an accommodating lens whose function is to enable patients to be without glasses.
The word “haptic” has been used to describe an attachment to intraocular lenses. The original intraocular lens consisted of a single optic. These single optic lenses, without any attachments, were first implanted in London by Harold Ridley in 1949. These lenses frequently de-centered and it was discovered that there was a need to center and fixate the lens optic in the vertical meridian of the eye. The first attachments to the optic were called “haptics”. They consisted of multiple flexible loops of various designs, J loops, C loops, closed loops and flexible radial arms. Later, these loops which became commonly referred to as “haptics” were replaced in some lens designs with plates, called “plate haptics”. Current plate haptic designs reduces the incidence of post-operative complications of cataract surgery, including retinal detachment and cystoid macular edema. Also, because of the more consistent location of the lens along the axis of the eye, the uncorrected post-operative visual acuities are superior to those of loop haptics.
During constriction of the circular ciliary muscle in an eye fitted with a plate haptic accommodating intraocular lens, the diameter of the ciliary muscle decreases and the muscle compresses the distal ends of the plate haptics, moving them centrally. Because uni-planar plate haptics tend to vault posteriorly when placed into the capsular bag, the central movement of the plate haptics causes their proximal end attached to the optic to move posteriorly and centrally. This posterior movement of the plates increases the vitreous cavity pressure behind the lens and its optic and simultaneously decreases the vitreous cavity pressure in the anterior chamber of the eye-and accommodates for near vision.
The current accommodating intraocular lenses utilize an oblong lens body design having flexible plate haptics connected to the lens optics by a single transverse hinge across the plate haptic. This promotes accommodation by allowing the optic to move forwards and backwards relative to the outer, or distal, ends of the plates. Such accommodating lenses are found in U.S. Pat. Nos. 5,476,514 and 5,496,366, both to Cumming, the disclosures of which are herein incorporated by reference. However, such designs do not permit adequate movement of the optic to a change in vitreous cavity pressure to allow many patients to read comfortably at near without glasses.
Current plate haptics are constructed of silicone, hydrogel or acrylic and are generally flexible. Due to this flexibility, current plate haptics tend to slightly buckle or deform when longitudinally compressed by the constriction of the ciliary muscle. This buckling reduces the possible pressure applicable by the plates on the vitreous cavity with constriction of the ciliary muscle.
Furthermore, when the accommodating lens plate haptic is fibrosed into the capsular bag of an eye after cataract surgery, sometimes several weeks or months following the surgery, a complication can occur. The lens can deform to a “Z” dislocated shape. This occurs when there is little sandwiching of the distal tip of the plate haptics between the remaining anterior and the posterior walls of the capsular bag.